Prevention and reversal of tolerance to nitroglycerine with N-acetylcysteine

A recent study demonstrated that the sulfhydryl donor N-acetylcysteine (NAC) potentiated hemodynamic responsiveness to nitroglycerine (NTG) in patients with ischaemic heart disease. The interaction between NTG and NAC in rings of bovine coronary artery was examined. Vasodilator responses to NTG were determined after elevation of tone with the thromboxane mimetic U46619 [(15S)-hydroxy-11 alpha, 9 alpha-(epoxymethano) prosta-5Z, 13E-dienoic acid]. NAC (1 microM-3 mM) induced no changes in tone of the preparation, but 10 microM NAC significantly potentiated responses to NTG (EC50 reduced from 0.69 +/- 0.19 microM to 0.22 +/- 0.06 microM; p less than 0.01). Increasing degrees of tolerance to NTG were produced at pH 7.4 by preincubating coronary rings with NTG in concentrations of 4.4 and 44 microM, and 0.22 mM. With 0.22 mM NTG, EC50 for subsequently administered NTG was increased to 11.0 +/- 1.8 microM (p less than 0.001 vs. control vessels). The degree of tolerance produced with this concentration of NTG was markedly attenuated by simultaneous (EC50 = 0.50 +/- 0.30 microM; p less than 0.001 vs. tolerant vessels) or subsequent (EC50 = 1.17 +/- 0.59 microM, p less than 0.001 vs. control vessels) incubation with 10 microM NAC. These data confirm that responses to NTG are modulated by sulfhydryl (or specifically cysteine) availability and suggest that in vitro tolerance to NTG is related to sulfhydryl (or cysteine) depletion. It is therefore possible that in vivo potentiation of NTG responses by NAC will be of clinical benefit in preventing or reversing loss of hemodynamic responsiveness to NTG.